读取内容取决于第一个字符的行 [英] Reading a line whose contents depends on the first character

问题描述

在Fortran中，实际的阅读方式是：

  A 1. 2. 3. 
  

如果第一个字符是A，但不读取：

  Z 
  

如果第一个字符是一个Z的例子。

如果我尝试读整行：

  read（1，*）char，number1，number2，number3 
  

然后如果数字缺失，则会发生错误。因此，我需要一种方式来读取该行上的A，并根据A或Z读取，如果需要，请阅读。

>解决方案

您可以随时阅读标志并在iolist中使用表达式来确定是否要读取更多内容。

az.f90：

 程序az 
隐式无
实数1，数字2，数字3 
字符azflag 
整数iunit 
 integer i 
 open（newunit = iunit，file ='az.txt'，status ='old'）
 do 
 number1 = -1 
 number2 = -1 
 number3 = -1 
 read（iunit，*，end = 10）azflag，（number1，number2，number3& 
，i = 1，merge（1,0，any（azflag == ['A'，'a']）））
 if（any（azflag == ['A'，'a']））then 
 write（*，*）'numbers read ！'
 else 
 write（*，*）'nothing read'
 end if 
 write（*，*）number1，number2，number3 
 end do 
 10继续
结束程序az 
  

az.txt：

  A 1. 2. 3. 
 Z 
a 4. 5. 6. 
z 
  

输出：

 数字已读！ 
 1.000000 2.000000 3.000000 
没有读取
 -1.000000 -1.000000 -1.000000 
数字读取！ 
 4.000000 5.000000 6.000000 
无读数
 -1.000000 -1.000000 -1.000000 
  

In Fortran, what would be the practical way to read:

 A 1. 2. 3.   

if the first character is an "A", but to not read the:

 Z

rest if the first character is a "Z" for example.

If I try to read the line at whole:

read(1,*)char, number1, number2, number3

then an error will occur if the numbers are missing. So I need a way to read an "A" stay on that line, and depending on the "A" or a "Z" read, if needed the rest.

解决方案

You can always read the flag and use an expression in the iolist to determine whether you want to read any more stuff.
az.f90:

program az
   implicit none
   real number1, number2, number3
   character azflag
   integer iunit
   integer i
   open(newunit=iunit,file='az.txt',status='old')
   do
      number1 = -1
      number2 = -1
      number3 = -1
      read(iunit,*,end=10) azflag, (number1,number2,number3 &
         ,i=1,merge(1,0,any(azflag==['A','a'])))
      if(any(azflag==['A','a'])) then
         write(*,*) 'numbers read!'
      else
         write(*,*) 'nothing read'
      end if
      write(*,*) number1, number2, number3
   end do
10 continue
end program az

az.txt:

 A 1. 2. 3.
 Z
 a 4. 5. 6.
 z

Output:

 numbers read!
   1.000000       2.000000       3.000000
 nothing read
  -1.000000      -1.000000      -1.000000
 numbers read!
   4.000000       5.000000       6.000000
 nothing read
  -1.000000      -1.000000      -1.000000

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